Adds complete API reference (api-reference.md) covering all endpoints: /api/stations (nearby search with postcode/lat+lng), /api/stats/searches (aggregated search stats), /api/prediction (7-day price forecast with multi-signal breakdown), and auth routes (register/login/logout/me). Includes request/response examples, error shapes, fuel type aliases, and signal structure details. Also removes unused AccountWidget from admin panel, disables BrentPriceChartWidget discovery, and adds searches stat to StatsOverviewWidget.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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